Field of the Invention
The present invention relates to a method for the provision of network services in a IMS (IP multimedia subsystem) type telecommunication network.
Description of the Related Art
As disclosed by the 3rd Generation Partnership Project (3GPP) in TS 23.002 V7.1.0 (2006-03), an IMS comprises CN (Core Network) elements for provision of IP multimedia services comprising audio, video, text, chat, etc. and a combination of them, delivered over the PS (Packet Switched) domain.
As disclosed by the 3rd Generation Partnership Project (3GPP) in TS 23.228 V7.5.0 (2006-09), when a user equipment (UE) attaches and makes itself available for access to IMS services by explicitly registering in the IMS, a Serving-Call Session Control Function (S-CSCF) shall be assigned to serve the UE.
As stated in the above mentioned technical specification TS 23.228, under chapter 4.6, the CSFC is an IMS entity that may take on various roles as used in the IMS. Proxy-CSFC (P-CSFC) is the first contact point within the IM (IP multimedia) CN subsystem. Its address is discovered by UEs using a mechanism named “Local CSCF Discovery”. Interrogating-CSFC (I-CSFC) is the contact point within an operator's network for all connections destined to a user of that network operator, or a roaming user currently located within that network operator's service area. Serving-CSCF (S-CSCF) performs the session control services for the UE. It maintains a session state as needed by the network operator for support of the services.
The assignment of an S-CSCF to a UE is performed according to a procedure named “IMS Registration”.
As disclosed in the above mentioned TS 23.228, under chapter 5.2.2.3, the IMS registration can be initiated after the registration to the access is performed, and after IP connectivity for the signalling has been gained from the access network. For the purpose of the registration information flows, the user is considered to be always roaming. For user roaming in their home network, the home network shall perform the role of the visited network elements and the home network elements. In particular, as shown in FIG. 1 (corresponding to FIG. 5.1 of said Technical Specification TS 23.228):
1. After the UE has obtained IP connectivity, it can start the IM registration by sending a Register information flow to the P-CSFC (e.g., Public User Identity, Private User Identity, home network domain name, UE IP address, Globally Routable User Agent URI (GRUU) Support Indication).
2. Upon receipt of the register information flow, the P-CSCF shall examine the “home domain name” according to the above mentioned “Local CSCF Discovery” mechanism to discover the entry point to the home network (i.e. the I-CSCF). The proxy shall send the Register information flow to the I-CSCF (P-CSCF address/name, Public User Identity, Private User Identity, P-CSCF network identifier, UE IP address). A name-address resolution mechanism is utilised in order to determine the address of the home network from the home domain name. The P-CSCF network identifier is a string that identifies at the home network, the network where the P-CSCF is located (e.g., the P-CSCF network identifier may be the domain name of the P-CSCF network).
3. The I-CSCF shall send a “Cx-Query/Cx-Select-Pull” information flow to the Home Subscriber Server (HSS) (Public User Identity, Private User Identity, P-CSCF network identifier).
The HSS shall check whether the user is already registered. The HSS shall indicate whether the user is allowed to register in that P-CSCF network (identified by the P-CSCF network identifier) according to the User subscription and operator limitations/restrictions, if any.
4. A “Cx-Query Resp/Cx-Select-Pull Resp” information flow is sent from the HSS to the I-CSCF. It shall contain the S-CSCF name, if it is known by the HSS, or the S-CSCF capabilities, if it is necessary to select a new S-CSCF. When capabilities are returned, the I-CSCF shall perform the selection function of a new S-CSCF based on the capabilities returned.
If the checking in HSS was not successful the Cx-Query Resp shall reject the registration attempt.
5. The I-CSCF, using the name of the S-CSCF, shall determine the address of the S-CSCF through a name-address resolution mechanism. The I-CSCF also determines the name of a suitable home network contact point, possibly based on information received from the HSS. I-CSCF shall then send the register information flow (P-CSCF address/name, Public User Identity, Private User Identity, P-CSCF network identifier, UE IP address) to the selected S-CSCF. The home network contact point will be used by the P-CSCF to forward session initiation signalling to the home network.
The S-CSCF shall store the P-CSCF address/name, as supplied by the visited network. This represents the address/name that the home network forwards the subsequent terminating session signalling to the UE. The S-CSCF shall store the P-CSCF Network ID information.
6. The S-CSCF shall send a “Cx-Put/Cx-Pull” information flow (Public User Identity, Private User Identity, S-CSCF name) to the HSS.
7. The HSS shall store the S-CSCF name for that user and return the information flow “Cx-Put Resp/Cx-Pull Resp” (user information) to the S-CSCF. The user information passed from the HSS to the S-CSCF shall include one or more names/addresses information which can be used to access the platform(s) used for service control while the user is registered at this S-CSCF. The S-CSCF shall store the information for the indicated user. In addition to the names/addresses information, security information may also be sent for use within the S-CSCF.
8. Based on the filter criteria, the S-CSCF shall send register information to the service control platform and perform whatever service control procedures are appropriate.
9. The S-CSCF shall return a 200 OK information flow (home network contact information, a GRUU) to the I-CSCF.
10. The I-CSCF shall send information flow 200 OK (home network contact information, a GRUU) to the P-CSCF. The I-CSCF shall release all registration information after sending information flow 200 OK.
11. The P-CSCF shall store the home network contact information, and shall send information flow 200 OK (a GRUU) to the UE.
Once it has successfully performed the IMS registration, a UE can access IMS services and make use of the services offered by an application server (AS) through the S-CSCF assigned thereto. A S-CSCF to AS interface is used to provide services residing in an AS.
As stated in TS 23.002, an application server (AS) offers either the basic logic for multimedia services or value added IM services and can reside either in the user's home network or in a third party location. The third party could be a network or simply a stand-alone application server. An application server can be, for example, a SIP (Session Initiation Protocol) application server, an OSA (Open Services Architecture) application server, or a CAMEL (Customised Application Mobile Enhanced Logic) IM-SSF (IM-Service Switching Function).
Therefore, according to what disclosed in the above cited technical specifications, a S-CSCF is assigned to serve a UE at the registration of the UE in the IMS. Then, when the UE makes a request for access to a specific service, the S-CSCF assigned thereto during the IMS registration serves the UE for the provision of said specific service.